Bearing thermal relief fan drive gear system assembly method

ABSTRACT

A method of assembling mating components includes the steps of heating an inner surface of a first cavity of a first part to generate a first expansion, heating an outer surface of a component surrounding an outer periphery of the first part to generate a second expansion of the component that corresponds to the first expansion of the first part, inserting a second part into the first cavity while the first part is in an expanded condition, and cooling the first part to contract around the second part.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/637,452 filed on Mar. 4, 2015.

BACKGROUND

A gas turbine engine typically includes a fan section, a compressorsection, a combustor section and a turbine section. Air entering thecompressor section is compressed and delivered into the combustionsection where it is mixed with fuel and ignited to generate a high-speedexhaust gas flow. The high-speed exhaust gas flow expands through theturbine section to drive the compressor and the fan section. A speedreduction device such as a gear assembly may be utilized to drive thefan section such that the fan section may rotate at a speed differentthan the turbine section so as to increase the overall propulsiveefficiency of the engine.

In such engine architectures, a shaft driven by the turbine sectionprovides an input to the gear assembly. The shaft may be constructedfrom multiple sections assembled together. Assembly of the various shaftsections may be performed utilizing press fits. A press fit assembly mayinclude heating of one part to allow another part to fit therein.Heating to expand one component is complicated if several components arewithin a heated region. Non-uniform heating of some portions of a shaftinterface can induce unwanted stress on parts, such as bearingassemblies. Accordingly, it is desirable to develop an assembly methodthat enables expansion by the application of heat without damage tosurrounding parts.

SUMMARY

In one exemplary embodiment, a method of assembling mating componentsincludes the steps of heating an inner surface of a first cavity of afirst part to generate a first expansion, heating an outer surface of acomponent surrounding an outer periphery of the first part to generate asecond expansion of the component that corresponds to the firstexpansion of the first part, inserting a second part into the firstcavity while the first part is in an expanded condition, and cooling thefirst part to contract around the second part.

In a further embodiment of the above, includes heating the inner surfacewith a first inductive coil disposed within the first cavity and heatingthe outer surface of the component with a second inductive coil disposedabout the outer surface.

In a further embodiment of any of the above, the first part includes afirst shaft including a splined interior surface and the second partincludes a second shaft including a splined exterior surface receivablewithin the splined interior surface of the first part.

In a further embodiment of any of the above, the first shaft includes acoupling shaft for driving a geared architecture and the second shaftincludes a shaft driven by a turbine section of a gas turbine engine.

In a further embodiment of any of the above, the component includes abearing assembly supporting rotation of the first part. The bearingassembly includes an inner race, an outer race and a bearing disposedthere

between and the method includes heating the bearing assembly to expandthe inner race and outer race in proportion to expansion of the firstpart.

In a further embodiment of the above, includes a housing supporting thebearing assembly. The method includes application of heat to the housingto generate expansion of the bearing assembly in proportion to expansionof the first part.

In a further embodiment of any of the above, includes detectingexpansion with a sensor to determine if a predetermined amount ofexpansion between the first part and the component has occurred toenable installation of the second part into the first part.

In a further embodiment of any of the above, the first part is heated toa first temperature and the component is heated to a second temperaturethat is different than the first temperature.

In another exemplary embodiment, a method of mating shaft sections for agas turbine engine, the method including the steps of assembling abearing assembly about an outer surface of a first shaft, heating aninner race of the bearing assembly, heating an outer race of the bearingassembly separately from heating of the inner race and at the same timeas heating the inner race, inserting a portion of a second shaft into acavity of the first shaft, and cooling the first shaft, the secondshaft, the inner race and the outer race of the bearing assembly suchthat the first shaft shrinks onto the second shaft.

In a further embodiment of the above, heating the inner race of thebearing assembly includes inserting a heating device into an innercavity of the first shaft to an axial location corresponding to aposition of the inner race on the outer surface of the first shaft andheating the inner race through the inner cavity of the first shaft.

In a further embodiment of any of the above, heating the outer race ofthe bearing assembly includes positioning a heating device about anouter surface of the outer bearing race and heating the outer bearingrace to expand the outer bearing race proportionate to expansion of theinner race.

In a further embodiment of any of the above, including expanding thecavity of the first shaft to provide a fit for a portion of the secondshaft.

In a further embodiment of any of the above, an interface between thecavity of the first shaft and an outer surface of the second shaftincludes a splined connection.

In a further embodiment of any of the above, including a first inductiveheating element received within the first cavity for imparting heat tothe first shaft and the inner bearing race and a second inductiveheating element disposed about the outer housing.

In a further embodiment of any of the above, including a housingsupporting the bearing assembly and heating of the outer bearing raceincludes heating the housing in an axial location corresponding to anaxial position of the outer bearing race.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of a gas turbine engine.

FIG. 2 is a schematic representation of an embodiment of a first shaftcomponent assembled to a second shaft

FIG. 3 is a schematic view of an example method of mating two shaftparts together.

FIG. 4 is another schematic representation of an embodiment of a heatingstep for assembly two shaft components.

FIG. 5 is a schematic representation of the mating step between firstand second shaft components.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 58 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 58 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 58 includes airfoils 60 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10.67 km). The flight condition of 0.8 Mach and35,000 ft (10.67 km), with the engine at its best fuel consumption—alsoknown as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—isthe industry standard parameter of lbm of fuel being burned divided bylbf of thrust the engine produces at that minimum point. “Low fanpressure ratio” is the pressure ratio across the fan blade alone,without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressureratio as disclosed herein according to one non-limiting embodiment isless than about 1.45. “Low corrected fan tip speed” is the actual fantip speed in ft/sec divided by an industry standard temperaturecorrection of [(Tram ° R)/(518.7° R)]0.5. The “Low corrected fan tipspeed” as disclosed herein according to one non-limiting embodiment isless than about 1150 ft/second (350 m/second).

The example gas turbine engine includes the fan 42 that comprises in onenon-limiting embodiment less than about twenty-six (26) fan blades. Inanother non-limiting embodiment, the fan section 22 includes less thanabout twenty (20) fan blades. Moreover, in one disclosed embodiment thelow pressure turbine 46 includes no more than about six (6) turbinerotors schematically indicated at 34. In another non-limiting exampleembodiment the low pressure turbine 46 includes about three (3) turbinerotors. A ratio between the number of fan blades 42 and the number oflow pressure turbine rotors is between about 3.3 and about 8.6. Theexample low pressure turbine 46 provides the driving power to rotate thefan section 22 and therefore the relationship between the number ofturbine rotors 34 in the low pressure turbine 46 and the number ofblades 42 in the fan section 22 disclose an example gas turbine engine20 with increased power transfer efficiency.

The example gas turbine engine 20 includes the geared architecture 48that drives the fan section 22. The geared architecture 48 is driven bythe turbine section 28 through a shaft 40. A coupling shaft 62 isdisposed between the shaft 40 and the geared architecture 48. Thecoupling shaft 62 includes features that can accommodate movement andmisalignment of the shaft 40 relative to the geared architecture 48. Theability to accommodate this misalignment enables the geared architecture48 to function and increases the efficiency of the geared architectureby reducing the amount of wear that may occur due to misalignment.

An interface between the coupling shaft 62 that transfers power into thegeared architecture 48 and the turbine shaft 40 is provided after thelow pressure compressor 44 and prior to the geared architecture 48. Thecoupling shaft 62 is connected to the geared architecture 48. Thecoupling shaft 62 is supported by a bearing assembly 64. The bearingassembly 64 is mounted outboard of the interface of the shaft 62 and theturbine shaft 40. It should be appreciated that assembly of the couplingshaft 62 to the shaft 40 is provided as a disclosed example, and thatthe method and structures disclosed are contemplated for use with anyinterface where two shafts or other structures are assembled together.

Referring to FIG. 2 with continued reference to FIG. 1, the shaft 40 iscoupled to the coupling shaft 62 through a splined interface 88. In thisexample, the shaft 40 includes splined portion 86 (FIG. 5) disposedabout an outer surface of a portion of the shaft 40. The coupling shaft62 includes an inner cavity 68 that includes a plurality of interiorsplines 70 (FIGS. 3 and 5) that mate with the splined portion 86 on theshaft 40. Assembly of the shafts is provided as a tight press fitsometimes referred to as a snap fit. The press fit between the shaft 40and the coupling shaft 62 is accomplished by heating the coupling shaft62 to expand the cavity 68 that enables insertion of the splined portion86 of the shaft 40.

The assembly sequence for assembling the gas turbine engine requiresthat a bearing assembly 64 is first assembled to an outer surface of thecoupling shaft 62. In this example, the bearing assembly 64 includes aninner race 72 that is supported on an outer surface of the couplingshaft 62. The bearing assembly 64 further includes an outer race 74 anda bearing 76 disposed between the inner and outer races 72, 74. Thebearing 76 may include bearings disposed within a cage. The outer race74 is in turn supported by a housing 66. The housing 66 supports thebearing assembly 64 that in turn supports rotation of the coupling shaft62.

Heating of this complex stack of parts complicates the assembly process.Heating the coupling shaft 62 causes a thermal expansion. Because theinner bearing race 72 and the outer bearing race 74 are not uniformlyheated, they do not expand in a uniform manner and can induce stresseson and between the inner race 72 and the outer race 74. The non-uniformheating can induce undesired stresses on the bearing assembly.

Accordingly, the example method provides steps for expanding thecoupling shaft 62 to receive a portion of the turbine shaft 40 withoutdamaging or otherwise imparting undue stresses and strains on theexample bearing assembly 64. The temperature range is defined to providea desired temperature differential that is does not damage the bearingassembly 64.

Referring to FIG. 3 with continued reference to FIG. 1, the examplemethod begins by inserting inductive coils 78 into the cavity 68 of thecoupling shaft 62. A second set of inductive coils 80 are disposed aboutan outer surface of the housing 66 at an axial location that correspondsto the position of the bearing assembly 64 on the coupling shaft 62. Apower source 82 powers the inductive coils 78, 80. It should beunderstood that inductive coils 78, 80 are shown by way of example, andother heating devices and structures could be utilized and are withinthe contemplation of this disclosure.

The disclosed example assembly method includes the initial step ofassembling the bearing assembly 64 to the outer surface of the couplingshafts 62. The interior inductive coil 78 is then inserted into thecavity 68 of the coupling shaft 62. In this example, the inner cavity 68includes the splines 70 that mate with the corresponding splined portion86 of the shaft 40. An outer or second inductive coil 80 is placedagainst the housing 66 at an axial location proximate to the bearingassembly 64. Application of heat with both the inner and outer inductivecoils 78, 80 provides a uniform thermal expansion of the coupling shaft62 and the bearing assembly 64.

The second inductive coil 80 heats the housing 66 and also the outerbearing race 74 such that the coupling shaft 62, the inner bearing race72 and the outer bearing race 74 are all expanded uniformly. The shaft62 may be of a different material than the material utilized for thebearing races 72, 74 and therefore include different thermal properties.Accordingly, the specific energy and heat induced by the secondconductive coil 80 may be different than the heat induced by the firstinductive coil 78. In this example, heat imparted into the couplingshaft 62 and the inner and outer bearing races 72 and 74 is matched toprovide a uniform amount of the thermal expansion that does not incurundue stresses on any of the components. The amount of thermal expansionis dependent on the thermal properties of each of the components andtherefore the heat induced by the first coil 78 may be different thanthe heat induced by the second coil 80. Moreover, the second coil 80 mayimpart an increased amount of heat to expand the outer race 74 in amanner that will relieve stresses and not impart undue strain on thebearings 76 that is disposed between the inner and outer races 72, 74.

A sensor 84 is disposed proximate to the coupling shaft 62 and bearingassembly 64. The sensor 84 can be utilized to detect a range ofexpansion to determine if the coupling shaft 62 is expanded sufficientlyto receive the shaft 40 or the sensor 84 may be utilized to determinewhen a specific temperature has been obtained by each of the components.As appreciated, a specific temperature can be correlated with a desiredexpansion rate and thereby determining a temperature of a specificcomponent can provide information indicative of the amount of expansionthat has occurred.

Once the coupling shaft 62 is expanded to a desired diameter determinedto provide for acceptance of the splined portion 86, the inductive coils78 and 80 are removed and the spline portion 86 of the shaft 40 isinserted into the cavity 68. It should be understood that although asplined interface is disclosed, other interfaces as are known within theart are within the contemplation of this disclosure.

Once the shaft 40 is inserted into the coupling shaft 62, the shafts 40,62 and bearing assembly 64 are cooled such that coupling shaftconstricts around the shaft 40 to form a snap or tight press fit. Thetight press fit is desirable as it provides for a secure innerconnection between the torque transferring shafts.

Accordingly, the example method of assembling mating shaft componentsenables assembly of two shaft components in complex tolerance stack upconditions.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this disclosure. For that reason, the followingclaims should be studied to determine the scope and content of thisdisclosure.

What is claimed is:
 1. A method of assembling mating componentscomprising the steps of: heating an inner surface of a first cavity of afirst part to generate a first expansion; heating an outer surface of acomponent surrounding an outer periphery of the first part to generate asecond expansion of the component that corresponds to the firstexpansion of the first part; inserting a second part into the firstcavity while the first part is in an expanded condition; and cooling thefirst part to contract around the second part.
 2. The method as recitedin claim 1, including heating the inner surface with a first inductivecoil disposed within the first cavity and heating the outer surface ofthe component with a second inductive coil disposed about the outersurface.
 3. The method as recited in claim 1, wherein the first partcomprises a first shaft including a splined interior surface and thesecond part comprises a second shaft including a splined exteriorsurface receivable within the splined interior surface of the firstpart. The method as recited in claim 3, wherein the first shaftcomprises a coupling shaft for driving a geared architecture and thesecond shaft comprises a shaft driven by a turbine section of a gasturbine engine.
 5. The method as recited in claim 4, wherein thecomponent comprises a bearing assembly supporting rotation of the firstpart, the bearing assembly including an inner race, an outer race and abearing disposed therebetween and the method includes heating thebearing assembly to expand the inner race and outer race in proportionto expansion of the first part.
 6. The method as recited in claim 5,including a housing supporting the bearing assembly, wherein the methodincludes application of heat to the housing to generate expansion of thebearing assembly in proportion to expansion of the first part.
 7. Themethod as recited in claim 1, including detecting expansion with asensor to determine if a predetermined amount of expansion between thefirst part and the component has occurred to enable installation of thesecond part into the first part.
 8. The method as recited in claim 1,wherein the first part is heated to a first temperature and thecomponent is heated to a second temperature that is different than thefirst temperature.